Photographic reversal development



Patented Aug. 21, 1934 UNITED STATES PATENT- OFFICE on-the-Rhine,

Germany,

assignor to Alia Ansco Corporation, Binghamton, N. Y., a corporation of New York No Drawing. Application January 15, 1932,

Serial No. 586,969. In Germany I 3 Claims.

odourless sulfur compound which does not color the finished picture or the binding agent and is capable of forming developable nuclei of silver sulfide. Whereas the known alkaline developer when the second exposure is omitted, produces a blackening oifthe silver halide only after at least minutes, the alkaline developer mixed with a small quantity of an odourless I sulfur compound, for instance, thiosinamine or ,thiourea, produces the silver picturealready after one minute. The sulfur compound alone in the low concentration, in which it is present, would not be able to blacken the silver halide. Odourless sulfur compounds are, besides the thiosinamine already mentioned, thiourea and other sulfur compounds capable of forming germs of silver sulfide. t The following example illustrates the invenion: 1000 cc. of the known metol-hydroquinone-developer, as it is utilized in the reversal development {or the first negative development, are mixed with 0.5 gram of thiosinamine. The silanuary 17,

ver halide which remains in the Layer after the treatment with the reversal bath consisting of bichromate and sulfuric acid is blackened by the odourless solution in less than one minute. The tint of the silver picture is very similar to that of a picture produced with a pure alkali sulfide.

The requisite odorless sulfur compound may be mixed with the developer in solid form, so that a solid developer in accordance with my invention may be placed on the market.

The reversal process may be carried out in any known manner, so, for instance, after the firstdeveloping operation a clearing bath may be introduced.

What I claim is:

1. In the photographic reversal process the step which comprises, after a first development and bleaching of a photographic material, effecting a second development with an alkaline developer containing a small quantity of an odourless sulfur compound capable of forming germs of silver sulfide. v

2. In the photographic reversal process the step which comprises, after a first development and bleaching 01' a photographic material, eftecting a second development with an alkaline developer containing a small quantity of thiosinamine.

3. In the photographic reversal process the 

